@barbudo2005
If this option is disabled, Dark Reader will check if a website has native dark theme, and will call for it.
If this option is enabled, Dark Reader will ignore native dark theme and convert the light version of the website to dark according to Dark Reader's inversion instructions.
So if the website is actively checking my OS theme (which is dark), and serves me dark version anyway, then this option will just change what kind of dark theme I'm getting: I will be served either the original dark theme, or Dark Reader's inverted dark theme.
AFAIK, there is no way to request original Light theme using Dark Reader.
Now, thanks to Vivaldi's new setting, I can force all websites to be Light in Vivaldi, and have Dark Reader decide which websites and when to request/convert to dark.